This invention relates to hindered-hydroxyl functional (meth)acrylate monomers containing significant amounts of the corresponding di(meth)acrylate, and to copolymer compositions including the same. These hindered-hydroxyl functional (meth)acrylate monomers are particularly useful in preparing polymers that can be cured with a variety of crosslinking agents to prepare compositions including coatings, adhesives, inks, sealants and the like.
(Meth)acrylate monomers, this term including acrylates, which contain significant amounts of di(meth)acrylate are know to suffer from premature crosslinking or gel formation during subsequent polymerization.
Typically, hindered-hydroxyl functional (meth)acrylate monomers are prepared by (i) direct esterification of a diol compound with methacrylic acid or acrylic acid, (ii) reaction of a diol compound with methacrylic anhydride or acrylic anhydride, and (iii) transesterification of a diol compound with alkyl methacrylate or alkyl acrylate. When the hydroxyl functional (meth)acrylate monomers are prepared, it is difficult to separate the starting diol from the various acrylates formed because both the starting diol and monomeric isomers have similar boiling points. To circumvent this difficulty, it is known in the art to carry the reaction to a higher degree of completion to minimize the amount of unreacted diol in the final reaction mass. However, this also increases the amount of what was considered undesirable di(meth)acrylate in the final product; which must be removed by distillation to prevent premature crosslinking during subsequent polymerization.
Applicants have discovered that when the (meth)acrylate involved is sterically hindered, the presence of significant amounts of di(meth)acrylate does not result in gel formation during polymerization. This discovery significantly reduces the cost of production of these type of monomers by eliminating the added step of separating the normally desirable mono(meth)acrylates from any di(meth)acrylate that may be present.
The present invention allows for preparation of (meth)acrylate copolymers from hindered-hydroxyl (meth)acrylates having di(meth)acrylate contents significantly above those known in the prior art, without premature crosslinking or gel formation.